1. Field of the Invention
The present invention relates to a method for driving a high quality, low power consumption display device, including a digital memory for each pixel and intended for use with small information terminals.
2. Description of Related Art
In recent years, liquid crystal display devices have commonly been used in small information terminals, such as portable telephones or electronic notebooks, because they are light, thin, and have low power consumption. Further, since the small information terminals are generally battery operated, reducing power consumption is a matter of great importance.
Especially with regards to portable telephones, there is a need for devices that can display data in a standby mode at low power consumption. As one example of a technique adapted to realize these needs, a liquid crystal display device is disclosed in Japanese Unexamined Patent Publication No. 2001-264814. During a standby period (hereinafter referred to as a still picture display period), this liquid crystal display device, which includes a digital memory for each pixel, achieves a dramatic reduction in power consumption by halting all peripheral driver circuits other than an alternating-current driver circuit that supplies an alternating current for driving the liquid crystal.
Since in this liquid crystal display device the liquid crystal is driven by an alternating current when a still picture is displayed, two memory switch elements are provided on the output side of the digital memory. When, in accordance with two independent memory control signals, these memory switch elements are alternately turned on for each frame, the output/inverted output (binary output) of the digital memory are alternately applied to a pixel electrode, and in accordance with this cycle the potential of the opposite electrode is inverted. Therefore, for a pixel for which the phase of the potential of the pixel electrode corresponds to that of the potential of the opposite electrode, no voltage is applied to the liquid crystal layer, while for a pixel for which the phase of the potential of the pixel electrode is the inverse of that of the potential of the opposite electrode, a voltage is applied to the liquid crystal layer. By repeating this operation, the liquid crystal can be driven by an alternating current.
However, since a wiring resistor and a wiring capacitor exist along a memory control signal line over which the memory control signals are transmitted, the rise time and fall time of the memory control signal waveform may be delayed. Due to this delay when the two memory switch elements are turned on at the same time, the output and inverted output of the digital memory are applied to the pixel electrode at the same time, therefore a normal write voltage is unable to be applied to the liquid crystal layer, and a still picture display failure occurs.